No abstract

Safeners have been widely used to reduce phytotoxicity to crops, thus serving as an alternative weed control strategy. Benoxacor and fenclorim safeners have the potential to protect plants from herbicide phytotoxicity by increasing glutathione S-transferase (GST) activity within the plant. The study aimed to evaluate the safening effect of benoxacor and fenclorim on tomato against selected herbicides applied POST. The experiment was conducted in a greenhouse in a completely randomized designed with four replications in a 9 × 3 factorial scheme, where Factor A consisted of eight herbicides including a nontreated control, and Factor B consisted of two safeners including a nontreated control. The herbicide treatments were sulfentrazone (0.220 kg ai ha−1), fomesafen (0.280 kg ai ha−1), flumioxazin (0.070 kg ai ha−1), linuron (1.200 kg ai ha−1), metribuzin (0.840 kg ai ha−1), pyroxasulfone (0.220 kg ai ha−1), and bicyclopyrone (0.040 kg ai ha−1). Safener treatments consisted of benoxacor (0.67 g L−1) and fenclorim (10 µM). Tomato seeds were immersed in safener solution before sowing and herbicides were applied when tomato plants were at the 3-leaf stage, or 25 days after sowing. Visible injury was scored at 3, 7, 14, and 21 d after application (DAA), and shoot biomass was recorded 21 DAA. Seed treatment with fenclorim reduced injury caused by imazamox and bicyclopyrone by 5.5 and 1.3 times, respectively, whereas benoxacor reduced the injury from bicyclopyrone 1.3 times. In addition, tomato plants pretreated with fenclorim showed a lesser reduction in biomass after application of imazamox, fomesafen, and metribuzin, whereas plants pretreated with benoxacor showed lesser biomass reduction after metribuzin application. Thus, the use of safeners promotes greater crop selectivity, allowing the application of herbicides with different mechanisms of action on the crop.

Weed-suppressive crop cultivars are a potentially attractive option in weed management strategies (IWM). A greenhouse study was conducted at the R. R. Foil Plant Science Research Center, Starkville, MS, to assess the potential weed-suppressive ability of 17 tomato cultivars against Palmer amaranth (Amaranthus palmeri S. Wats), yellow nutsedge (Cyperus esculentus L.), and large crabgrass (Digitaria sanguinalis L.). The experiment was a completely randomized design, with four replications, and was repeated twice. The height, chlorophyll, and dry weight biomass of the weeds were measured 28 days after sowing. Weed suppression varied greatly among tomato cultivars. The most significant effect of tomato interference was recorded on Palmer amaranth, and the least reduction was observed with yellow nutsedge plants. Cultivars 15 and 41 reduced Palmer amaranth height and biomass by about 45 and 80%, respectively, while cultivar 38 reduced 60% of the chlorophyll percentage. Large crabgrass plants were 35% shorter in the presence of cultivar 38 and had a biomass reduction of 35% in the presence of cultivar 38. Under tomato interference, a minimal effect was observed in chlorophyll, height, and biomass of yellow nutsedge seedlings. Factoring all parameters evaluated, cultivars 38 and 33 were most suppressive against Palmer amaranth and large crabgrass.

Annual bluegrass (Poa annua L.) is a problematic weed in turfgrass that has evolved resistance to 12 different herbicide sites of action. The mitotic inhibiting herbicide pronamide has both pre-and postemergence activity on susceptible annual bluegrass populations, but on certain resistant populations, postemergence activity is hypothetically compromised due to lack of root uptake or due to an unknown foliar resistance mechanism. Spray droplet size may affect foliar and soil deposition of pronamide, thus potentially explaining variation in population control or differential shoot and root uptake. Greenhouse experiments were conducted to quantify pronamide, flazasulfuron, and pronamide + flazasulfuron (a common tank mixture) deposition on annual bluegrass as affected by spray-droplet size. Five droplet sizes (200, 400, 600, 800, and 1,000 μm) were sprayed in an enclosed spray chamber on two-to three-leaf stage annual bluegrass plants. Fluorescent dye was added to each treatment solution to quantify the effects of herbicide and spray droplet size on herbicide deposition. Results indicate that spray droplet size affects deposition of pronamide and flazasulfuron, applied alone and in combination, on annual bluegrass. The highest foliar deposition was produced with 400-μm spray droplets in pronamide treatments and with 200 μm spray droplets in flazasulfuron and pronamide + flazasulfuron treatments. The addition of flazasulfuron to pronamide did not affect herbicide deposition when compared with pronamide-alone treatments. Results suggest that 200-to 400-μm spray droplets are optimal for foliar deposition of pronamide. Alternatively, larger droplet sizes may facilitate better soil deposition of pronamide where root uptake is optimal.

A greenhouse dose-response study was conducted to determine the tolerance of three wild tomato accessions (TOM199, TOM198, TOM300) in comparison to a commercial cultivar (Better Boy) against the dicamba application at five rates (0, 70, 140, 210, and 280 g ae ha-1) at 14 and 28 days after treatment (DAT). Several physiological traits were evaluated at 0, 1, 3, 5, and 7 DAT. Wild accessions and cultivar were killed at all rates above 70 g ae ha-1 at 14 and 28 DAT, which is why differences between accessions and cultivar were only evident at 70 g ae ha-1. The GR50 (the herbicide rate that causes 50% reduction in dry weight) of Better Boy was 4.4 g ae ha-1 at 28 DAT, and this cultivar was approximately 11-fold more sensitive than wild accessions. At 7 DAT, the levels of H2O2 for wild accessions were lower than Better Boy up to 5 at 70 g ae ha-1 of dicamba. Furthermore, wild accessions showed lower herbicide absorption than Better Boy at all dicamba doses at 1, 3, and 7 DAT. All the three wild accessions expressed tolerance to the dicamba application at the dose of 70 g ae ha-1. At the same time, Better Boy and wild accessions were susceptible to dicamba application at rates of 140, 210, and 280 g ae ha-1.